Characterizing the role of pancreatic progenitors in regeneration. Our goals are focused on identifying pathways used to generate new beta-cells either during development or regeneration. It is hoped that this approach will identify targets tha can be exploited in the treatment of diabetes. As there is a high degree of conservation in the molecular mechanisms that control vertebrate pancreas development and function, we have turned to the zebrafish as an alternative model system to study beta-cell biology and regeneration. The zebrafish has a remarkable capacity for regenerating tissues following organ damage and we have shown that this ability extends to the insulin producing beta-cells of the pancreas. We reason that it will be easier and faster to study mechanisms involved in tissue recovery in an organism that can readily regenerate. From work done in other systems, it is apparent that different methods of tissue injury can promote different regenerative responses. The most efficient way to learn about the cells and signals involved in regeneration will be to utilize different experimental models of pancreas injury. To these ends our lab has developed: i) An efficient transgenic method to specifically ablate the beta-cells while being able to simultaneously image the remaining islets; ii) Chemically induced pancreatitis destroying the acinar tissue; iii) A surgical procedure to remove a large portion of the pancreas (partial pancreatectomy). In order to ascertain the cells involved in regeneration, we developed the tools and methods to perform long-range lineage tracing in the zebrafish. With this technique, we identified the pancreatic progenitors in the larvae that give rise to endocrine and centroacinar cells of the adult fish. With this technology in hand and the experience gained, we can now fate map different pancreatic cell types and ascertain their role in facultative regeneration following tissue damage from any of our injury models. Many aspects of regeneration recapitulate molecular pathways and mechanisms used during development. For instance, we showed that Notch-signaling was important in regulating beta-cell formation during development and we recently demonstrated that Notch-signaling is dramatically up-regulated following adult pancreas injury. To find more pathways, we carried out a chemical screen for drugs that induce the formation of precocious islets in larval fish. This work led to the identification of several novel pathways involved in beta-cell differentiation. With pharmaceutical and newly developed genetic methods in hand, we can manipulate all these pathways mentioned and study their effects on both pancreas development and regeneration. This work is aimed at ascertaining if these pathways can be manipulated to induce adult beta-cell neogenesis, and provide the platform for future studies in mammalian models. PUBLIC HEALTH RELEVANCE: Characterizing the role of pancreatic progenitors in regeneration We aim to speed up the discovery of therapeutic factors for diabetes by applying the advantages that the zebrafish offers. This model organism has very similar pancreas biology to humans, yet is extremely capable of regenerating the insulin producing beta-cells following pancreas injury in adults. Our lab has developed the novel tools required to study pancreas regeneration, identify the cellular origins of new beta-cells and elucidate the molecular pathways that underlie the zebrafish's unique ability to regenerate beta-cell mass.